As is known in the art of water treatment for microbiological control, a deficiency of chlorine, of hypochlorites, and of certain halogenated organic water-treating agents is the formation, during usage, of undesirable disinfection by-products. These by-products are undesirable both from the standpoint of environmental concerns and also from the standpoint of toxicological considerations.
Certain 1,3-dihalo-5,5-dialkylhydantoins have been found to be effective as biocides for aqueous systems such as industrial cooling water, recreational water, and wastewater.
Persons using biocidal agents in the biocidal treatment of water customarily, if not universally, refer to xe2x80x9cfree chlorinexe2x80x9d level as a measure of biocidal control. To achieve xe2x80x9cfree chlorinexe2x80x9d levels in water treatment, solid materials are often preferred because of their high weight percent activity. N,Nxe2x80x2-bromochloro-5,5-dimethylhydantion (BCDMH) has been one of the most widely-used solid sources of xe2x80x9cfree chlorinexe2x80x9d for water treatment. One of the features emphasized for BCDMH by suppliers of BCDMH is that in use, the combined chlorine from the biocide regenerates xe2x80x9cfree chlorinexe2x80x9d by reaction with inactive bromide species formed during the water treatment operation. In other words, the chlorine atom in the initial N,Nxe2x80x2-bromochloro-5,5-dialkylhydantoin is said to be a precursor for additional xe2x80x9cfree chlorinexe2x80x9d for sanitation purposes.
In use, BCDMH hydrolyzes into HOBr and HOCl both of which register as xe2x80x9cfree chlorinexe2x80x9d species in commonly-used standard test procedures. These methods for determining xe2x80x9cfree chlorinexe2x80x9d levels in treated water, involve use of a reagent known as DPD (i.e., N,Nxe2x80x2-diethyldiphenylenediamine) and a buffer, and the results of such analyses are commonly used, if not universally used, as the basis for determining the quantity of a halogen-containing microbiocidal agent to be used for water treatment. Heretofore, consumers of BCDMH have only been concerned with the level of xe2x80x9cfree chlorinexe2x80x9d provided by a given quantity of that biocidal material. What has not been realized by such consumers is the amount of xe2x80x9ctotal chlorinexe2x80x9d being utilized in order to achieve the requisite xe2x80x9cfree chlorinexe2x80x9d level. As a consequence, the consumer has not had available a yardstick by which to determine the true economic efficiency of using BCDMH as a biocidal agent in the treatment of water. To achieve optimum economic efficiency, the consumer should have available for use a biocidal agent in which the amount of xe2x80x9cfree chlorinexe2x80x9d released into the water corresponds closely to the xe2x80x9ctotal chlorinexe2x80x9d content of the biocidal agent.
In the event a biocidal agent provides a relatively small amount of xe2x80x9cfree chlorinexe2x80x9d in relation to its xe2x80x9ctotal chlorinexe2x80x9d content, it has been deemed necessary to utilize a relatively large amount of such agent in order to achieve microbiological control. This in turn means high levels of halogenated materials are released into the environment. If on the other hand, a biocidal agent could provide to the water an amount of xe2x80x9cfree chlorinexe2x80x9d that closely corresponds to the xe2x80x9ctotal chlorinexe2x80x9d content of the biocidal agent, effective microbiological control could be realized by use of much smaller dosages and with consequent minimal adverse impact upon the environment.
This invention involves, inter alia, the discovery that there is a substantial disparity between the xe2x80x9cfree chlorinexe2x80x9d level and the xe2x80x9ctotal chlorinexe2x80x9d level delivered to the water when using BCDMH as a biocidal agent. Thus the consumer of BCDMH as a water treating agent unknowingly has been paying for a relatively ineffective microbiocidal agent. Moreover, such consumer has been contributing unknowingly to the release of undesirable quantities of halogenated materials to the environment.
This invention further involves, inter alia, the discovery that the level of xe2x80x9cfree chlorinexe2x80x9d available from 1,3-dibromo-5,5-dimethylhydantoin (DBDMH), especially when used in water having a pH of at least about 8.0, closely approximates its xe2x80x9ctotal chlorinexe2x80x9d content. Consequently the use of one or more water-soluble dialkyldibromohydantoins such as DBDMH as a water treating agent, especially when used in the treatment of industrial cooling water, is highly effective from an economic standpoint and highly desirable from an environmental standpoint. That is to say, the dosage levels of water-soluble dialkyldibromohydantoins such as DBDMH needed to provide effective microbiological control with respect to such undesirable organisms and pathogens as bacteria, algae, and biofilms, are relatively low compared to dosage levels of BCDMH required for the same degree of control, especially in industrial cooling water. Moreover, the levels of halogenated materials released to the environment are much smaller when using a water-soluble dialkyldibromohydantoin such as DBDMH as compared to BCDMH.
Accordingly, this invention provides in one of its embodiments a method of providing microbiological control in an aqueous medium such as recreational water, industrial cooling water, process water, or wastewater, and preferably in water having a pH of at least about 8.0 such as cooling water and/or eradication or reduction of biofilm on a surface in contact with such aqueous medium, which method comprises introducing into the aqueous medium a microbiocidally effective amount of at least one 1,3-dibromo-5,5-dialkylhydantoin in which one of the alkyl groups in the 5-position is a methyl group and the other alkyl group in the 5-position contains in the range of 1 to 4 carbon atoms (DBDAH), (i) the molar quantity of the DBDAH introduced being less than the molar quantity of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH) that would be required to effect the same degree of microbiological control in such medium, (ii) the quantity of DBDAH introduced into such aqueous medium releasing an amount of xe2x80x9cfree chlorinexe2x80x9d that is greater than the amount of xe2x80x9cfree chlorinexe2x80x9d that would be released in such medium by an equimolar quantity of BCDMH, and (iii) the amount of xe2x80x9cfree chlorinexe2x80x9d released by the quantity of such at least one DBDAH introduced into such aqueous medium being greater than the amount of xe2x80x9cfree chlorinexe2x80x9d that could be predicted to be released by that quantity of DBDAH on the basis of the amount of xe2x80x9cfree chlorinexe2x80x9d that would be released in such medium by an equimolar quantity of BCDMH. The most preferred DBDAH used in this embodiment is 1,3-dibromo-5,5-dimethylhydantoin (DBDMH).
In another of its embodiments this invention provides a method of effecting microbiocidal activity in water preferably but not necessarily having a pH of at least about 8.0, which method comprises providing in such water using a 1,3-dibromo-5,5-dialkylhydantoin (DBDAH) microbiocidal agent in which one of the alkyl groups of the DBDAH in the 5-position is a methyl group and the other alkyl group in the 5-position contains in the range of 1 to 4 carbon atoms, a microbiocidally effective amount of xe2x80x9cfree chlorinexe2x80x9d that is greater than could be predicted from the amount of xe2x80x9cfree chlorinexe2x80x9d that would be released by an equimolar quantity of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH) in such water, while using a smaller molar quantity of the DBDAH than the molar quantity of BCDMH required to release such microbiocidally effective amount of xe2x80x9cfree chlorinexe2x80x9d. 1,3-Dibromo-5,5-dimethylhydantoin (DBDMH) is also the most preferred microbiocidal agent employed in this embodiment.
A further embodiment of this invention is a composition having microbiocidal activity, which composition comprises water preferably but not necessarily having a pH of at least about 8.0 to which has been added a microbiocidally effective quantity of a 1,3-dibromo-5,5-dialkylhydantoin (DBDAH) in which one of the alkyl groups is a methyl group and the other alkyl group contains in the range of 1 to 4 carbon atoms, (i) the molar quantity of the DBDAH added being less than the molar quantity of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH) that would be required to effect the same degree of microbiocidal activity in that water, (ii) the quantity of DBDAH added releasing an amount of xe2x80x9cfree chlorinexe2x80x9d that is greater than the amount of xe2x80x9cfree chlorinexe2x80x9d that would be released in that water by an equimolar quantity of BCDMH, and (iii) the amount of xe2x80x9cfree chlorinexe2x80x9d released by the amount of DBDAH added being greater than the amount of xe2x80x9cfree chlorinexe2x80x9d that could be predicted to be released by DBDAH on the basis of the amount of xe2x80x9cfree chlorinexe2x80x9d that would be released in that water by an equimolar quantity of BCDMH. Here again, the most preferred DBDAH is 1,3-dibromo-5,5-dimethylhydantoin (DBDMH).
This invention as reflected for example by the above embodiments, involves a number of surprising features. First of all, it is surprising that to achieve a given level of microbiocidal effectiveness, especially in an aqueous medium with a pH of at least about 8.0, a smaller quantity of DBDAH such as DBDMH can be used than BCDMH. Heretofore the art has regarded BCDMH as being a biocidal agent of choice because of the levels of effectiveness achieved by use of that agent. Moreover, it is surprising that in an aqueous medium preferably but not necessarily with a pH of about 8.0 or higher, the amount of xe2x80x9cfree chlorinexe2x80x9d released by a DBDAH such as DBDMH is greater than the amount of xe2x80x9cfree chlorinexe2x80x9d released by an equimolar quantity of BCDMH. At best the expectation would be that there could be no significant difference, and thus that there would be no appreciable difference, in these respective amounts of xe2x80x9cfree chlorinexe2x80x9d. Furthermore, not until comparative testing of water samples with a pH of greater than about 8.0 containing, respectively, equimolar quantities of DBDMH or BCDMH for xe2x80x9cfree chlorinexe2x80x9d using Hach Method 8021 (copyright 1997, by Hach Company) and for xe2x80x9ctotal chlorinexe2x80x9d using Hach Method 8167 (copyright 1997, by Hach Company), and converting the mg/L Cl2 xe2x80x9cfree chlorinexe2x80x9d values from the tests to percentages of the mg/L Cl2 xe2x80x9ctotal chlorinexe2x80x9d values from the tests, was the unpredictable superiority of DBDMH in releasing larger amounts of xe2x80x9cfree chlorinexe2x80x9d than the equimolar quantity of BCDMH discovered. Prior to such testing there was no way of predicting the existence this superiority.
As a consequence of the above surprising features of this invention it is now possible to achieve the same microbiocidal effect on or control of bacteria, algae, biofilm, and like microbiological entities as given by BCDMH but using smaller molar amounts of one or more of the above described 1,3-dibromo-5,5-dialkylhydantoins such as DBDMH, and at the same time significantly reducing the amounts of halogenated materials to be released to the environment. Alternatively, greater microbiocidal control of bacteria, algae, biofilm, and like microbiological entities can be achieved using one or more of the above described 1,3-dibromo-5,5-dialkylhydantoins such as DBDMH in the same molar quantity as BCDMH, or even somewhat less molar quantity of one or more such 1,3-dibromo-5,5-dialkylhydantoins than BCDMH.
Another embodiment of this invention is a method for determining a quantity of a 1,3-dibromo-5,5-dialkylhydantoin such as DBDMH to be used in microbiocidal treatment of water preferably but not necessarily having a pH of at least about 8.0. The method comprises (i) determining the xe2x80x9cfree chlorinexe2x80x9d concentrations of samples of said water containing respectively BCDMH and the DBDAH, (ii) determining the xe2x80x9ctotal chlorinexe2x80x9d values of samples of said water containing respectively BCDMH and DBDAH, and (iii) determining respectively for BCDMH and DBDAH the relative extent of hydrolysis to species which register as xe2x80x9cfree chlorinexe2x80x9d. Such determinations can be accomplished by dividing the value obtained for xe2x80x9cfree chlorinexe2x80x9d by the value obtained for xe2x80x9ctotal chlorinexe2x80x9d and multiplying the quotient by 100 to obtain the percentage of hydrolysis to xe2x80x9cfree chlorinexe2x80x9d. Use of this method enables the amount of DBDAH to be used in achieving the target dose of xe2x80x9cfree chlorinexe2x80x9d. By xe2x80x9ctarget dosexe2x80x9d is meant the dose deemed suitable by the water treater to effect microbiocidal control in the water being subjected to treatment. In conducting this embodiment of the invention, any suitable method of determining xe2x80x9cfree chlorinexe2x80x9d and xe2x80x9ctotal chlorinexe2x80x9d can be used, but in the event of any conflicting data as between different parties, Hach Method 8021 (copyright 1997) for xe2x80x9cfree chlorinexe2x80x9d and Hach Method 8167 (copyright 1997) for xe2x80x9ctotal chlorinexe2x80x9d shall be used. For example, a given water treater may deem a slug dose of, say, 0.2 mg/L of xe2x80x9cfree chlorinexe2x80x9d to be sufficient for maintaining microbiocidal control in a given body of water. Knowing the extent of hydrolysis as determined by use of this invention, and also the total volume of the body of water, the water treater can determine an amount of solid DBDAH to apply in a slug dose to achieve effective microbiocidal control while at the same time without using an undue excess of DBDAH.
In another of its embodiments, this invention provides a method of effecting biocidal activity in water preferably but not necessarily having a pH of at least about 8.0, which method comprises providing in such water using a 1,3-dibromo-5,5-dialkylhydantoin (DBDAH) biocidal agent an amount of xe2x80x9cfree chlorinexe2x80x9d that is greater than could be predicted from the amount of xe2x80x9cfree chlorinexe2x80x9d provided by an equimolar amount of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH), as determinable by comparative testing as follows:
a) determining the amount of species of the DBDAH and of BCDMH which register respectively as xe2x80x9ctotal chlorinexe2x80x9d using Hach Method 8167 (copyright 1997, by Hach Company);
b) determining the amount of species of the DBDAH and of BCDMH which register respectively as xe2x80x9cfree chlorinexe2x80x9d using Hach Method 8021 (copyright 1997, by Hach Company); and
c) determining respectively for the DBDAH and BCDMH the relative extent of hydrolysis to species which register as xe2x80x9cfree chlorinexe2x80x9d.
The foregoing method can be applied for treating water for microbiological control and/or for biofilm eradication.
Another embodiment is water preferably but not necessarily having a pH of at least about 8.0 in which microbiological and/or biofilm activity is minimized if not eliminated by the addition thereto of an amount of xe2x80x9cfree chlorinexe2x80x9d using an above-described 1,3-dibromo-5,5-dialkylhydantoin (DBDAH) biocidal agent where the amount of xe2x80x9cfree chlorinexe2x80x9d actually present in the water is greater than could be predicted from the amount of xe2x80x9cfree chlorinexe2x80x9d provided by an equimolar amount of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH), as determinable by comparative testing as follows:
a) determining the amount of species of the DBDAH and of BCDMH which register respectively as xe2x80x9ctotal chlorinexe2x80x9d using Hach Method 8167 (copyright 1997, by Hach Company); and
b) determining the amount of species of the DBDAH and of BCDMH which register respectively as xe2x80x9cfree chlorinexe2x80x9d using Hach Method 8021 (copyright 1997, by Hach Company); and
c) determining respectively for the DBDAH and BCDMH the relative extent of hydrolysis to species which register as xe2x80x9cfree chlorinexe2x80x9d.
The microbiological control and/or for biofilm eradication in the water involves effective biocidal activity against such organisms and pathogens as bacteria, algae, and biofilms.
Other embodiments, features, and advantages of this invention will be still further apparent from the ensuing description and appended claims.